Firefox 3 offers the ability to save web pages directly without any external applications. However, you need to expose this functionality which not currently in the front end.

PrintPDF is a free Firefox 3 add-on which allows users on Windows and Linux to print web pages to PDF. This add-on will use your default printer options when formatting the page for PDF generation. The add-on just exposes functionality not currently in the front end.

Output samples (compared with CutePDF):

Neowin

PrintPDF (Size: 2.41 MB)

CutePDF (Size: 1.06 MB)

Phoenix (spacecraft) Wikipedia

PrintPDF (Size: 2.53 MB)

CutePDF (Size: 826 KB)

Output size from PrintPDF seems to be bigger compared with the output from CutePDF. If you want a stylish PDF output form web pages, this extension might not suitable for you. As you can see from the samples, websites with colors and heavy design will be poorly printed. You might need to use external applications such as CutePDF to PDF print those websites. But, if you don't have the time to download and install CutePDF, or you are just PDF printing Wikipedia articles, this Firefox 3 add-on might suitable for you.

[Firefox Add-on (for Firefox 3 only): PrintPDF]

See also:
Bypassing Megaupload Country Slot Limit
Easily Download Flash Video From Websites
How to Save a Web Page as Image